Jet lag is a temporary desynchronization of the body’s internal clock caused by rapidly crossing time zones. The circadian clock (suprachiasmatic nucleus of the hypothalamus) regulates the sleep-wake cycle, body temperature, and the secretion of melatonin and cortisol on a 24-hour cycle. During a transmeridian flight, this clock remains set to the original time for 2 to 5 days, creating a discrepancy between internal biological rhythms and the local time at the destination. Characteristic symptoms include difficulty falling asleep, waking up during the night, daytime sleepiness, and fatigue —which are more severe than a simple lack of sleep because they affect all biological rhythms.
The direction of travel determines the severity of jet lag. Flights to the east (advancing the time: Paris → Tokyo) require falling asleep and waking up earlier than usual, going against the natural tendency of the human circadian clock (slightly longer than 24 hours). Flights heading west extend the day and are better tolerated. The rule of thumb: 1 day of recovery per hour of time difference when traveling east, 0.5 to 0.7 days when traveling west. Mental focus and cognitive performance are the first functions to be affected—an important factor for business travel.
Melatonin is the gold standard for treating jet lag—in fact, it is the only officially recognized indication by the EFSA (minimum 0.5 mg). Its action is chronobiotic (it shifts the circadian phase) and non-sedative. Two protocols depending on the direction of the flight:
Vitamin B6 (a cofactor in the synthesis of serotonin and endogenous melatonin) is commonly included in jet lag formulas to optimize natural nighttime production.
Light is the most powerful circadian synchronizer—it inhibits melatonin and advances or delays the body clock depending on the time of exposure. A light therapy lamp (10,000 lux, 20–30 minutes) is an essential complement to melatonin for accelerating resynchronization. Eastbound flight: bright light in the morning (local time) + darkness in the evening. Westbound flight: light in the late afternoon and evening (local time). Chronobiology apps (Timeshifter) calculate the optimal exposure times based on the specific flight. Any residual difficulty falling asleep after 3 days of adjustment warrants short-term herbal support (eschscholtzia, valerian).
Three phases of a comprehensive strategy. Before the flight (2–3 days): gradually shift your bedtime by 1 hour per day toward the destination time zone, maintain optimal hydration, and avoid alcohol, which disrupts sleep. During the flight: set your watch to the destination time as soon as you board; sleep if it’s nighttime at your destination (eye mask + earplugs + flash melatonin); stay awake if it’s daytime. After arrival: Stay awake until the local bedtime even if you’re exhausted; expose yourself to natural light according to the East/West protocol; take melatonin at the local bedtime. Jet lag involving fewer than 3 time zones generally does not require an active protocol—recovery occurs spontaneously within 1 to 2 days.
Jet lag is not the only chronobiological disorder associated with travel. Shift work (night shifts, rotating shifts) causes chronic circadian desynchronization through the same mechanisms as jet lag—with documented long-term metabolic and cardiovascular consequences. Motion sickness shares with jet lag a component of autonomic nervous system dysregulation—intense post-travel fatigue can combine both phenomena. Social jet lag (going to bed and waking up at very different times depending on the day of the week) is a form of weekly jet lag that affects 70% of adolescents. For any travel-related fatigue combining physical exhaustion and circadian disorientation, adaptogenic herbs (rhodiola, ginseng) and a recovery regimen provide effective support. People who regularly experience discomfort while traveling may also suffer from motion sickness, which sometimes combines with jet lag on long-haul flights.
